The simple answer would appear to be NO, you cannot gain more than the weight of the food you eat. Even if the food is salty and "binds" water in your body, either that water is already in your body contributing to your existing weight, and so no net gain; or you have to drink additional water, which is added to the weight of the food you eat. Even if you absorb some nominal amount of water by breathing (and I can't believe that's a significant amount, as you'll perish of dehydration if you don't drink fluid -- breathing in even humid air won't sustain you). So, unless the principal of conservation of mass has been discredited, you cannot gain more than the weight of your food (and liquid) intake. If you stand on a scale after eating (and drinking) all you will, you will not see your weight increase unless/until you resume eating.